1. Field of the Invention
The present invention relates to an organic electroluminescent display.
2. Description of the Related Art
Organic electroluminescent (organic EL) displays are self-emitting type thin displays, and have advantages of display performance such that high in visibility, and small in viewing angle dependency, as compared with liquid crystal displays. Further, in addition to the advantages of capable of making weight light and thinning, they have the possibility of realizing new shapes of displays that have been unrealized hitherto by using flexible substrates.
Organic EL displays have excellent characteristics as described above. However, although organic EL displays are excellent in viewing angle dependency as compared with liquid crystal displays, the refractive index of each layer including a light-emitting layer constituting the displays is generally higher than the refractive index of air, and since the refractive indexes are different, emission spectrums are different due to the angles to the displays by a light interference effect. This causes a tin variation depending on the viewing angle of the viewer, and may influence viewing angle characteristics.
Further, for the purpose of the improvement of frontal luminance, the use of a photo-resonance effect by the reflection on the surface between the electrodes positioned on both sides of the light-emitting layer, or the use of a prism sheet or the like is exemplified. In that case, the influence of viewing angle dependency is conspicuous.
As a means for improving viewing angle dependency, a method of using light scattering means is disclosed. For examples an organic EL display whose viewing angle characteristic is improved by providing a color filter and a light scattering means on the side for collecting light of the organic EL device is disclosed (e.g., refer to JP-A-11-329742 (The term “JP-A” as used herein refers to an “unexamined published Japanese patent application”.)). Specifically, as the scattering means, dispersing inorganic fine particles in the color filter, or providing a light scattering layer wherein inorganic fine particles are dispersed in contiguous to the color filter is disclosed.
Further, an organic EL display provided with a light scattering layer containing light scattering particles on the side to collect lights from the light-emitting layer to improve a viewing angle dependency is disclosed (e.g., refer to JP-A-2002-270365).
Further, for the improvement of viewing angle characteristics, it is proposed to provide a diffusing layer having haze of 80% or more (e.g., refer to JP-A-2003-173877). Specifically, a method of forming a scattering layer on a fluorescent layer by spin coating is shown. However, a light scattering property of the light scattering layer that is preferred for the improvement of viewing angle characteristics is not always sufficient by merely controlling haze.